Digital scales of current design utilize automatic zero tracking techniques which eliminate the need for frequent operator intervention to readjust the tare weight. Such automatic zero tracking usually involves measuring sequential signals representative of the tare weight and continually replacing older signals with newer signals until such time as a load is placed on the pan. When the load is placed on the pan, the latest signal or signals would then be stored to be subsequently subtracted from the gross weight.
Prior methods of tracking have been with an empty pan only; consequently when a weight is left on a pan for any significant duration, deviation from zero can take place either as a result of electronic or load cell drifts. With typical load cell scales, significant change in the reading takes place after a heavy load is applied due to the creep of the load cell; however, the change in indicated weight immediately after the load is applied is unaffected. Thus, when a load is left on a scale and creep takes place, immediately after the load has been removed the zero reading has been displaced by the same change as the creep. In time, the scale would uncreep in a manner symmetrical with the original creep and depending on the original creep's rate and size, but a significant amount of time may elapse before zero is recaptured.
It therefore would be advantageous to have a system whereby the tare weight, or zero, is continually updated whether a load is upon the pan or not. With such a system, not only would time be saved in waiting until the tare weight has reached equilibrium after a load is removed from the pan, but also at the time the load is upon the pan the gross weight would not be accurate if creep and drift are not taken into account.